Solid state light sources based on thermally conductive luminescent elements containing interconnects

ABSTRACT

Solid state light sources based on LEDs mounted on or within thermally conductive luminescent elements provide both convective and radiative cooling. Low cost self-cooling solid state light sources can integrate the electrical interconnect of the LEDs and other semiconductor devices. The thermally conductive luminescent element can completely or partially eliminate the need for any additional heatsinking means by efficiently transferring and spreading out the heat generated in LED and luminescent element itself over an area sufficiently large enough such that convective and radiative means can be used to cool the device.

REFERENCE TO PRIOR APPLICATION

This application is a continuation of U.S. application Ser. No.14/071,609 filed Nov. 4, 2013, which claims benefit as a continuation ofU.S. application Ser. No. 13/572,608 filed Aug. 10, 2012, which claimsthe benefit of U.S. Provisional Patent Application Ser. No. 61/574,925,which was filed on Aug. 11, 2011, which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

This invention relates to solid state light sources based on LEDsmounted on or within thermally conductive luminescent elements, whichprovide both convective and radiative cooling. Low cost, self-coolingsolid state light sources can be realized by also integrating theelectrical interconnect of the LEDs and other semiconductor devices. Thethermally conductive luminescent element can be used to completely orpartially eliminate the need for any additional heatsinking means byefficiently transferring and spreading out the heat generated in LED andluminescent element itself over an area sufficiently large enough suchthat convective and radiative means can be used to cool the device.

Solid luminescent ceramic plates are disclosed in Born, U.S. Pat. No.4,849,639, as scintillators for the conversion of shorter wavelengthphotons to longer wavelength photons. Born does not disclose the use ofthe ceramic plates to convert narrowband emission from solid stateemitters into broadband visible light sources.

Ce:YAG in ceramic, single crystal, and powder forms have been used sincethe early 1970s to convert blue wavelengths to yellow wavelengths forefficient coupling of flashlamp outputs into laser rods at Bell Labs andother institutions. Again, the use of these materials to convert blue/UVsolid state emitters into broadband white light sources is notdisclosed.

The formation of transparent and translucent luminescent YAG ceramicsare disclosed in Cusano, U.S. Pat. No. 4,421,671, and Greskovich, U.S.Pat. No. 4,466,930. The use of these materials as scintillators, CRTfaceplates, and X-ray screens is disclosed but not their use in solidstate lighting.

The use of solid wavelength conversion elements to form self coolinglight sources in which the solid wavelength conversion element is aceramic, single crystal, composite and layered solid material isdisclosed in Zimmerman, U.S. Pat. No. 7,285,791. Zimmerman discloses theuse of solid wavelength conversion elements to form solid state lightsources in U.S. Pat. No. 7,804,099. The use of high emissivity surfacesis not disclosed.

Mueller-Mach et al. in U.S. Pat. No. 6,696,703 disclose the depositionof a thin film phosphor directly on the LED die. However, as-depositedthin film phosphors have relatively poor wavelength conversionefficiency. A high-temperature annealing step is required in order toproperly activate the phosphor. This annealing step can damage thesemiconductor layers of the LED. In addition, the absorptioncross-sections of most thin film phosphors are low, especially for blueand near ultraviolet (UV) excitations typically used within solid-statelighting. It is neither economical nor practical in most cases to createa sufficiently thick layer of luminescent material directly on the LED.Another drawback to depositing a phosphor directly on the LED die isthat a large portion of the light generated within a deposited phosphorlayer can be trapped due to total internal reflectance. The needtherefore exists for a method to utilize high performance phosphorswithin an LED package such that the best phosphor can be usedefficiently (e.g. with sufficient quantity, minimal backscatter, andmaximum light extraction). The need also exists for a method tofabricate high efficiency phosphors without damaging the LEDsemiconductor layers. In addition, high emissivity is not disclosed.

Another important aspect of phosphors relates to characterization andoverall device efficiency. Phosphors are typically characterized interms of quantum efficiency and Stokes shift losses. As an example, apowder phosphor layer is deposited on a glass surface and excited. Theluminescence is measured as a function of excitation energy and theresult is usually compared to a standard phosphor of known quantumefficiency. The losses associated with Stokes shift can be subtractedand the result would be the intrinsic quantum efficiency. Severalproblems exist with this method of characterization such asbackscattered light, coating thickness variability and light trapping.In the case of phosphor powders, the majority of the generated light canescape from the phosphor particles due to their substantially sphericalnature and to scattering centers located on or in the material itself.The main problem measuring the efficiency of phosphor powders isbackscattering of the light from thick samples. For deposited phosphorfilms or grown phosphor boules, however, the problem of measuring thephosphor efficiency is affected by light extraction. The majority of thelight generated in the phosphor can be trapped within the materialitself due to total internal reflection. Several approaches have beenused to solve the total internal reflection problem including variousroughening techniques and shaping approaches. In these cases, theoverall efficiency becomes as much a function of the extraction means asthe conversion efficiency. Deposited phosphor films have the addedcomplication of a secondary substrate material with its associatedindices and losses.

Mayer et al. in U.S. Pat. No. 6,565,770 describe thin interferencepigment flakes that can be made on a flexible substrate and thenmechanically removed by flexing the substrate. The dichroic reflectorsdiscussed are used in security enhancement on money and other decorativeoptical effects. The use of luminescent materials is discussed but isrelated to the formation of a particular optical effect such as UVillumination for security markings. No explanation for improving theoutput efficiency of LEDs or other light emitting devices is discussedand no device based on integrating the phosphor layer with theexcitation source to form an efficient solid-state lighting element isdisclosed.

The use of flake-like phosphors is also discussed by Aoki et al. in U.S.Pat. No. 6,667,574 for use in plasma displays, but the patent againlacks any reference to solid-state lighting applications or methods toenhance their output. In addition, the above two applications are verymuch cost driven because of the large areas typically required in makinga plasma display or the marking of money or decorative items. In orderto maximize the performance of these wavelength-converting materialshigh temperature processing is preferred.

Mueller-Mach et al. in U.S. Pat. No. 6,630,691 disclose a thinsingle-crystal phosphor substrate onto which an LED structure isfabricated by epitaxial growth techniques. However, single-crystalphosphor substrates are expensive and finding a single crystal phosphorsubstrate that has the proper lattice match to allow the growth of theLED structure can be difficult.

Ng et al. in US Patent Application No. 20050006659 disclose a planarsheet of a single-crystal phosphor that is placed over the outputsurface of an LED as a portion of a preformed transparent cap. However,single-crystal phosphor sheets must be grown by epitaxial processes orsliced from bulk single crystals of phosphor material. Single crystalphosphor sheets are therefore too expensive for most practicalapplications. Planar sheets of polycrystalline phosphors are notdisclosed in US Patent Application No. 20050006659. Bonding the planarsheet of a single-crystal phosphor directly to the surface of the LED toimprove heat dissipation in the phosphor sheet is also not disclosed.

LEDs unlike conventional light sources such as incandescent bulbs cannoteffectively cool themselves. As such additional heatsinking or coolingmeans are required to prevent overheating. This increases the cost ofnot only the light sources due to shipping costs and materials costs butalso the fixtures that use those light sources. In general, the needexists for articles and means, which allow LEDs to be used without theneed for additional heatsinking means.

It is desirable to minimize the temperature difference between thejunction or active region of the semiconductor device and the ambientatmosphere to effectively cool small semiconductor devices. It is alsodesirable to minimize the surface area needed to dissipate the heatgenerated by the semiconductor devices to the ambient atmosphere. Whilehigh thermal conductivity materials can be used to spread the heat outover a very large area, these high thermal conductivity materials comewith the addition of significant weight and cost. In conventional LEDdevices several layers of interconnect exist between the LED die and thefinal light source. This approach is used because the lighting fixturemanufacturers have historically not been required or had the capabilityto wirebond, flipchip attach or even solder components into theirfixtures. Also the need to regularly replace light sources such asincandescent bulbs has led to a wide range of quick change interconnectslike sockets and pin based connector. Lightweight self cooling solidstate light sources would offer significant benefits to fixturemanufacturers. Incandescent bulbs for instance are very lightweightgenerating over 1000 lumens while weighing only 50 grams and as such canbe easily held in place using even simple pins and sockets. For thetypical LED sources, this is not the case. The added weight of theheatsink and the need for a low resistance thermal connection betweenthe LED package and the heatsink necessitates the use of complexmultiple level interconnects. The need exists for LED light sources,which are lightweight and easily incorporated into a wide range oflighting fixtures without the need for additional heatsinking or coolingmeans.

As is well known to those skilled in the art, phosphor conversion istypically used to broaden the narrow band emission of LEDs to moreclosely match the sun or incandescent spectrum. This is usually done viaphosphor powders mixed into an organic matrix. Using this conventionalapproach, the heat generated in the phosphor powders is thermallyisolated from the ambient by the organic matrix.

For example, blue InGaN LEDs are routinely coated with a thin organiclayer containing phosphor powders. The organic material typicallyconsists of a silicone or epoxy. As the LED efficiency and flux densityhas increased, more of the thermal losses are localized in the phosphorpowders. Unfortunately, thermal conductivity of the luminescent layer ismainly determined by the thermal conductivity of the organic matrixmaterial, which is typically around 0.1 W/m/K. Typically a 50 microncoating thickness for the luminescent organic layer prevents highscatter losses created by the index of refraction difference between thephosphor powder and organic matrix material. Conversely, sufficientphosphor powder must be used to convert the shorter wavelengthexcitation to longer wavelength emission this is typically controlled bythe loading level, which is the ratio of the percentage of phosphorpowder to the percentage of organic matrix material. A lower loadinglevel of the phosphor powder reduces the thermal conductivity and ahigher loading level limits the thickness of coating due to scatterlosses.

Generically it is difficult to remove a significant amount of heat outof the phosphor powders, let alone the LEDs themselves, while they arein a low thermal conductivity matrix. Their luminescent efficiencytypically decreases as the phosphor powders get hotter. This luminescentinefficiency has spurred the development of remote phosphor approaches,which reduce the thermal load on the phosphor powders by moving thephosphor powder farther away from the LED and thereby reducing the fluxdensity per unit area on the powder. This remote phosphor approachhowever increases the source size, amount of phosphor powder required,forms a thermal barrier around the LEDs, and creates a large volumelight source.

In addition, organic systems are susceptible to blue and UV radiationdue to the photostability of the C—H bonds which define an organicsystem. Photostabilization of especially transparent optical systemsunder intense solarization has limited the long-term use of transparentorganics (plastics) in greenhouse and other outdoors applications. Thesolar constant is approximate 1000 optical watts per square meter, withless than 10% of that having a wavelength short enough tophotochemically attack the C—H bond. A typical blue LED in solid statelighting applications will output up to 1 optical watt per squaremillimeter of which virtually all the wavelengths emitted are capable ofadversely affecting the C—H bonds of organic materials. Theseirradiation levels represent four order of magnitude higher fluxdensities than greenhouse films experience. Accordingly, inorganicsolutions are more desirable than organic solutions for thermalconductivity and photostability standpoints.

All wavelength conversion materials and semiconductor devices exhibittemperature dependent efficiency curves. Thermal roll-off occurs forCe:YAG around 150 degrees C. Alternately, AlinGaP red diodes and InGaNblue die both exhibit some roll-off as the junction temperature exceeds100 degrees C. It therefore becomes critical that the heat generatedwithin a solid state lighting system is transferred to the surroundingambient using the lowest possible thermal resistance path. In the caseof natural convection cooling the amount of heat that can be transferredto the surrounding ambient (air) is determined by the natural convectionheat transfer coefficient, the area of the surface, and the temperatureof the surface relative to the surrounding air or ambient.

Radiative cooling can also contribute to cooling solid state lightingdevices if the temperature difference between the junction temperatureand the radiating surface is minimized over a sufficiently large highemissivity surface area of the lighting device. Proposed solutions suchas forced convection cooling, heatpipes, and even liquid cooling, eithermove the heat around or substantially increase the volume and weight ofthe light source. These solutions result in very low lumens/gram lightsources.

Historically, light sources have cooled themselves as stated earlier. Inthe case of incandescent and fluorescent tubes, the glass envelopesurrounding the sources, and the filament or arc itself transfers theexcess heat generated via convection and radiation. An incandescent bulbglass envelope can exceed 150 degrees C. and a halogen's quartz envelopemay exceed several hundred degrees celsius. Radiative power scales asthe fourth power of the temperature. A naturally convectively cooledsurface with a surface temperature of 50 degrees C. in a 25 degrees C.ambient will transfer only about 5% of its energy to the surroundingambient radiatively. A naturally convectively cooled surface with asurface temperature of 100 degrees C. can transfer 20% of its energy tothe surrounding ambient radiatively. The typical LED junctiontemperature for high powered devices can be over 120 degrees C. andstill maintain excellent life and efficiency. For surfaces withtemperatures less than 120 degrees C. the majority of the radiatedenergy is in the infrared with a wavelength greater than 8 microns.

The emissivity of the materials in the infrared varies greatly. Glasshas an emissivity of approximately 0.95 while aluminum oxide may be aslow as 0.23. Organics such as polyimides can have fairly high emissivityin thick layers. This however will negatively affect the transfer ofheat due to the low thermal conductivity of organics.

In order to maximize heat transfer to the ambient atmosphere, the needexists for luminescent thermally conductive materials which caneffectively spread the heat generated by localized semiconductor andpassive devices (e.g. LEDs, drivers, controller, resistors, coils,inductors, caps etc.) to a larger surface area than the semiconductordie via thermal conduction and then efficiently transfer the heatgenerated to the ambient atmosphere via convection and radiation. At thesame time, these luminescent thermally conductive materials mustefficiently convert at least a portion of the LED emission to anotherportion of the visible spectrum to create a self cooling solid statelight source with high L/W efficiency and good color rendering.

Heat generated within the LEDs and phosphor material in typical solidstate light sources is transferred via conduction means to a much largerheatsink usually made out of aluminum or copper. The temperaturedifference between the LED junction and heatsink can be 40 to 50 degreesC. The temperature difference between ambient and heatsink temperatureis typically very small given the previously stated constraints on thejunction temperatures of LEDs. This small temperature difference notonly eliminates most of the radiative cooling but also requires that theheatsink be fairly large and heavy to provide enough surface area toeffectively cool the LEDs. This added weight of the heatsink increasescosts for shipping, installation and in some cases poses a safety riskfor overhead applications.

Ideally, like incandescent, halogen, sodium, and fluorescent lightsources, the emitting surface of the solid-state light source would alsobe used to cool the source. Such a cooling source would have an emittingsurface that was very close to the temperature of the LED junctions tomaximize both convective and radiative cooling. The emitting surfaceshould be constructed of a material that exhibited sufficient thermalconductivity to allow for the heat from small but localized LED die tobe spread out over a sufficiently large enough area to effectively coolthe LEDs.

This invention discloses thermally conductive luminescent elementswithin solid state light sources, which overcome these issues.

SUMMARY OF THE INVENTION

This invention relates to solid state light sources based on LEDsmounted on or within thermally conductive luminescent elements. Thethermally conductive luminescent elements provide a substantial portionof the cooling of the LEDs using both convective and radiative coolingfrom the emitting surfaces. Electrical interconnect of the LEDs andother semiconductor devices based on opaque and/or transparentconductors create low cost self-cooling solid state light sources. Thelow cost self-cooling solid state light sources can have printed on,thick film printed silver conductors with a reflectivity greater than30%.

Briefly, and in general terms, the self cooling light source of theinvention comprises at least one light-emitting diode (LED) die; and atleast one thermally conductive luminescent element. The luminescentelement includes an electrical interconnect and performs multiplefunctions: as a wavelength converter, converting at least a portion ofthe light emitted by said LED die to a different wavelength range, as anoptical waveguide for light emitted by said LED die, and as a heatspreading element, spreading heat generated by said LED die over agreater cross-sectional area. Finally the luminescent element provides ahigh emissivity layer, for optimal coupling of emitted light from thelight source.

The thermally conductive luminescent element can be used to completelyor partially eliminate the need for any additional heatsinking means byefficiently transferring and spreading out the heat generated in LED andluminescent element itself over an area sufficiently large enough suchthat convective and radiative means can be used to cool the device. Inother words, the surface emitting light also convectively andradiatively cools the device. The thermally conductive luminescentelement also provides for the efficient wavelength conversion of atleast a portion of the radiation emitted by the LEDs.

The present invention may also be defined as a self cooling solid statelight source comprising at least one light-emitting diode (LED) die andat least one thermally conductive luminescent element bonded to the atleast one LED die; wherein heat is transmitted from the light source inbasically the same direction as emitted light. More specifically, lightis emitted from the LED die principally in a direction through the atleast one luminescent element, and heat generated in the light source istransmitted principally in the same direction as the direction of lightemission. Heat is dissipated from the light source by a combination ofradiation, conduction and convection from the at least one luminescentelement, without the need for a device heat sink.

Optionally, the luminescent thermally conductive element can providelight spreading of at least a portion of the radiation from the LEDsand/or radiation converted by the thermally conductive luminescentelements via waveguiding. A thermally conductive luminescent elementacts as a waveguide with alpha less than 10 cm-1 for wavelengths longerthan 550 nm. In this case, the LEDs with emission wavelengths longerthan 550 nm can be mounted and cooled by the thermally conductiveluminescent elements and also have at least a portion of their emissionefficiently spread out via waveguiding within the thermally conductiveluminescent element as well.

Thermally conductive luminescent elements with InGaN and AlInGaP LEDscan convert at least a portion of the InGaN spectrum into wavelengthsbetween 480 and 700 nm. Single crystal, polycrystalline, ceramic, and/orflamesprayed Ce:YAG, Strontium Thiogallate, or other luminescentmaterials emitting light between 480 and 700 nm and exhibiting an alphabelow 10 cm-1 for wavelengths between 500 nm and 700 nm can be athermally conductive solid luminescent light spreading element.

The mounting of InGaN and AlInGaP LEDs can form solid state extendedarea light sources with correlated color temperatures less than 4500 Kand efficiencies greater than 50 L/W and optionally color renderingindices greater than 80 based on these thermally conductive lightspreading luminescent elements.

One embodiment of this invention is a luminescent thermally conductivetranslucent element having a thermal conductivity greater than 1 W/m/Kconsisting of one or more of the following materials, alumina, ALN,Spinel, zirconium oxide, BN, YAG, TAG, and YAGG. Optionally, electricalinterconnects maybe formed on at least one surface of the luminescentthermally conductive translucent element to provide electricalconnection to the LED.

The luminescent thermally conductive element can have a thermalconductivity greater than 1 W/m/K and have an emissivity greater than0.2. A self cooling solid state light source can have at least oneluminescent thermally conductive element with a thermal conductivitygreater than 1 W/m/K and an emissivity greater than 0.2. A self coolingsolid state light source can have an average surface temperature greaterthan 50 degrees C. and a luminous efficiency greater than 50 L/W.Optionally, a self-cooling solid state light source can have an averagesurface temperature greater than 50 degrees C. and a luminous efficiencygreater than 50 L/W containing at least one luminescent thermallyconductive element with a thermal conductivity greater than 1 W/m/K andan emissivity greater than 0.2. A self-cooling solid state light sourcecan dissipate greater than 0.3 W/cm2 via natural convection cooling andradiation cooling.

Luminescent thermally conductive elements can be formed via thefollowing methods: crystal growth, sintering, coating, fusible coating,injection molding, flame spraying, sputtering, CVD, plasma spraying,melt bonding, and pressing. Pressing and sintering of oxides withsubstantially one phase will improve translucency based on a luminescentpowder. Alternately, a translucent element with a thermal conductivitygreater the 1 W/m/K and an alpha less than 10 cm-1 can be coated with aluminescent layer formed during the sintering process or after thesintering process. Single crystal or polycrystalline materials, bothluminescent and non-luminescent, can be the thermally conductiveluminescent element. Specifically TPA (transparent polycrystallinealumina), Spinel, cubic zirconia, quartz, and other low absorptionthermally conductive materials with a luminescent layer can be formedduring or after fabrication of these materials. Techniques such aspressing, extruding, and spatial flame spraying can form near net shapeor finished parts. Additional luminescent layers can be added to any ofthese materials via dip coating, flame spraying, fusing, evaporation,sputtering, CVD, laser ablation, or melt bonding. Controlled particlesize and phase can improve translucency.

Coatings can improve the environmental and/or emissivity characteristicsof the self-cooling light source, particularly if the coating is a highemissivity coating with and without luminescent properties. Singlecrystal, polycrystalline, ceramic, coating layers, or flame sprayed canbe used both as a coating and as the bulk material Ce:YAG, with a highemissivity or environmental protective coating. In particular,polysiloxanes, polysilazanes and other transparent environmentalovercoats can be applied via dip coating, evaporative, spray, or othercoating methods, applied either before or after the attachment of theLEDs. Additional luminescent materials can be added to these overcoatssuch as but not limited to quantum dots, luminescent dyes (such as Eljenwavelength shifter dyes), and other luminescent materials.

Wireless power transfer elements, power conditioning element, driveelectronics, power factor conditioning electronics, infrared/wirelessemitters, and sensors can be integrated into the self-cooling solidstate light source.

A self-cooling solid-state light source can have a luminous efficiencygreater than 50 L/W at a color temperature less than 4500K and a colorrendering index greater than 70. The self-cooling solid-state lightsource can have a surface temperature greater than 40 degrees C.,convectively and radiatively cooling more than 0.3 W/cm2 of light sourcesurface area, and having a luminous efficiency greater than 50 L/W.

A self-cooling solid-state light source can have a luminous efficiencygreat than 50 L/W at a color temperature less than 4500K and a colorrendering greater than 85 containing both blue and red LEDs. At leastone luminescent thermally conductive element with an alpha less than 10cm-1 for wavelengths longer than 500 nm is used in the self coolingsolid state light source containing at least one blue and at least oneLED with emission wavelengths longer than 500 nm. Additional luminescentmaterials in the form of coatings and/or elements including, but notlimited, to phosphor powders, fluorescent dies, wavelength shifters,quantum dots, and other wavelength converting materials, can furtherimprove efficiency and color rendering index.

Aspect ratios and shapes for the solid state light source can be,including but not limited to, plates, rods, cylindrical rods, spherical,hemispherical, oval, and other non-flat shapes. Die placement canmitigate edge effects and form more uniform emitters. Additionalscattering, redirecting, recycling, and imaging elements can be attachedto and/or in proximity to the solid state light source designed tomodify the far field distribution. Additional elements can be attachedto the solid state light source with a thermally conductivity greaterthan 0.1 W/m/K such that additional cooling is provided to the solidstate light source via conduction of the heat generated within the solidstate light source to the additional element and then to the surroundingambient. An external frame can provide mechanical support, can beattached to the solid state light source, and/or can provide an externalelectrical interconnect. Multiple solid state sources arranged with andwithout additional optical elements can generate a specific far fielddistribution. In particular, multiple solid state sources can bearranged non-parallel to each other such that surface and edgevariations are mitigated in the far field. A separation distance betweensolid state light sources faces of greater than 2 mm is preferred tofacilitate convective cooling. Mounting and additional optical elementscan enhance convective cooling via induced draft effects.

In this invention, thermally conductive luminescent elements on to whichsemiconductor devices are mounted are used to effectively spread theheat out over a sufficient area with a low enough thermal resistance toeffectively transfer the heat generated by the semiconductor devices andthe thermally conductive luminescent element itself to the surroundingambient by both convection and radiative means. In this invention, thesurface emitting light convectively and radiatively cools the device.

The thermally conductive luminescent element also provides for theefficient wavelength conversion of at least a portion of the radiationemitted by the LEDs. Optionally, the luminescent thermally conductiveelement can provide light spreading of at least a portion of theradiation from the LEDs and/or radiation converted by the thermallyconductive luminescent elements. The thermally conductive luminescentelements act as waveguides with alpha less than 10 cm-1 for wavelengthslonger than 550 nm. In this case the LEDs with emission wavelengthslonger than 550 nm can be mounted and cooled by the thermally conductiveluminescent elements and also have at least a portion of their emissionefficiently spread out via waveguiding within the thermally conductiveluminescent element as well.

Disclosed is a self cooling solid state light source containing anoptically transmitting thermally conductive element with a surfacetemperature greater than 50 degree C. and a surface area greater thanthe semiconductor devices mounted on the optically transmittingthermally conductive element. Even more preferably a self cooling solidstate light source containing at least one optically transmittingthermally conductive element with a surface temperature greater than 100degrees C. and a surface area greater than the surface area of themounted semiconductor devices. Most preferred is a self cooling solidstate light source containing at least one optically transmittingthermally conductive luminescent element with an average thermalconductivity greater than 1 W/m/K. As an example, YAG doped with 2%Cerium at 4 wt % is dispersed into an alumina matrix using spray drying.The powders are pressed into a compact and then vacuum sintered at 1500degrees C. for 8 hours, followed by hot isostatic pressing at 1600degrees C. for 4 hours under argon. The material is diamond saw dicedinto 1 mm thick pieces which are ½ inch×1 inch in area. The parts arelaser machined to form interconnect trenches into which silver paste isscreen printed and fired. The fired silver traces are then lapped toform smooth surface to which direct die attach LED die are soldered.Pockets are cut using the laser such that two pieces can be sandwichedtogether thereby embedding the direct die attach LED die inside twopieces of the ceramic Ce:YAG/alumina material. In this manner, a selfcooling light source is formed. The direct die attached LEDs areelectrically interconnected via the silver traces and thermallyconnected to the ceramic CeYag/alumina material. The heat generatedwithin the direct die attach LEDs and the ceramic Ce:YAG/aluminamaterial is spread out over an area greater than the area of the LEDs.In this example, power densities greater than 1 W/cm2 can be dissipatedwhile maintaining a junction temperature less than 120 degrees C. andsurface temperature on the ceramic CeYag/alumina material of 80 to 90degrees C. based on natural convection and radiative cooling. As such a¼ inch×½ inch solid state light source can emit over 100 lumens withoutany additional heatsinking or cooling means.

Materials with emissivities greater than 0.3 are preferred to enhancethe amount of heat radiated of the surface of the solid state lightsource. Even more preferable emissivity greater than 0.7 for surfacetemperatures less than 200 degrees C. A naturally convectively cooledsurface with a natural convection coefficient of 20 W/m2/k with asurface temperature of 50 degrees C. in a 25 degrees C. ambient willtransfer about 25% of its energy to the surrounding ambient radiativelyif the surface emissivity is greater than 0.8 and can dissipateapproximately 0.08 W/cm2 of light source surface area. A similarnaturally convectively cooled surface with a surface temperature of 100degrees C. can transfer 30% of its energy to the surrounding ambientradiatively and dissipate greater than 0.25 watts/cm2 of surface area. Asimilar naturally convectively cooled surface with a surface temperatureof 150 degrees C. can transfer 35% of the heat radiatively and dissipategreater than 0.4 watts/cm2. Given that solid state light sources canapproach 50% electrical to optical conversion efficiency and that thetypical spectral conversion is 300 lumens/optical watt using thisapproach a self cooling solid state light source can emit 75 lumens forevery 1.0 cm2 of light source surface area. As an example, a ¼inch×½inch×2 mm thick self cooling light stick can generate more than 150lumens while maintaining a surface temperature less than 100 degrees C.The typical LED junction temperature for high powered devices can beover 120 degrees C. and still maintain excellent life and efficiency.For surfaces with temperatures less than 120 degrees C. the majority ofthe radiated energy is in the infrared with a wavelength greater than 8microns. As such high emissivity coatings, materials, and surfaces whichare substantially transparent in the visible spectrum are preferredembodiments of self cooling light sources.

The emissivity of the materials in the infrared varies greatly. Glasshas an emissivity of approximately 0.95 while aluminum oxide may bebetween 0.5 and 0.8. Organics such as polyimides can have fairly highemissivity in thick layers. This however will negatively affect thetransfer of heat due to the low thermal conductivity of organics. Assuch high thermal conductivity high emissivity materials and coating arepreferred. High emissivity/low visible absorption coatings are describedin J. R. Grammer, “Emissivity Coatings for Low-Temperature SpaceRadiators”, NASA Contract NAS 3-7630 (30 Sep. 1966). Various silicatesare disclosed with emissivity greater than 0.85 and absorptions lessthan 0.2.

In order to maximize heat transfer to the ambient atmosphere, the needexists for luminescent thermally conductive materials which caneffectively spread the heat generated by localized semiconductor andpassive devices (e.g. LEDs, drivers, controller, resistors, coils,inductors, caps etc.) to a larger surface area than the semiconductordie via thermal conduction and then efficiently transfer the heatgenerated to the ambient atmosphere via convection and radiation. At thesame time, these luminescent thermally conductive materials mustefficiently convert at least a portion of the LED emission to anotherportion of the visible spectrum to create a self cooling solid statelight source with high L/W efficiency and good color rendering.Conventional wavelength converters in both solid and powder form aresubstantially the same size as the LED die or semiconductor devices.This minimizes the volume of the luminescent material but localizes theheat generated within the luminescent element due to stokes losses andother conversion losses. In present day solid state light sourcesapproximately 50% of the heat generated is within the luminescentmaterial. By using a thermally conductive luminescent element with lowdopant concentration which also acts as a waveguide to the excitationlight emitted by the LEDs, the heat generated by the luminescentconversion losses can be spread out over a larger volume. In addition amore distributed light source can be generated rather localized pointsources as seen in conventional LED packages. In this manner the needfor addition diffusing and optical elements can be eliminated orminimized. As such the use of luminescent thermally conductive elementswith surface area greater than the semiconductor devices mounted on theluminescent elements is a preferred embodiment.

Heat generated within the LEDs and phosphor material in typical solidstate light sources is transferred via conduction means to a much largerheatsink usually made out of aluminum or copper. The temperaturedifference between the LED junction and heatsink can be 40 to 50 degreesC. The temperature difference between ambient and heatsink temperatureis typically very small given that significant temperature drop occursfrom the LED junction and the heatsink surfaces. This small temperaturedifference not only eliminates most of the radiative cooling but alsorequires that the heatsink be fairly large and heavy to provide enoughsurface area to effectively cool the LEDs. The larger the heatsink, thelarger the temperature drop between the LED junction and the surface ofthe heatsink fins. For this reason, heatpipes and active cooling is usedto reduce either the temperature drop or increase the convective coolingsuch that a smaller heatsink volume can be used. In general, the addedweight of the heatsink and/or active cooling increases costs forshipping, installation, and in some cases poses a safety risk foroverhead applications.

Ideally, like incandescent, halogen, sodium, and fluorescent lightsources, the emitting surface of the solid-state light source would alsobe used to cool the source. Such a cooling source would have an emittingsurface that was very close to the temperature of the LED junctions tomaximize both convective and radiative cooling. The emitting surfaceshould be constructed of a material that exhibited sufficient thermalconductivity to allow for the heat from small but localized LED die tobe spread out over a sufficiently large enough area to effectively coolthe LEDs. In this invention this is accomplished by spreading the heatgenerated within the luminescent element out over a larger volume, usinga thermal conductivity luminescent element that spreads the heatgenerated in the semiconductor devices used via conduction over a largersurface area than the semiconductor devices, and maximizing theradiative and convective cooling by high emissivity coatings, increasedsurface area, and higher surface temperatures created by efficientcoupling of the heat to the surface of the self cooling light source.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B depict side views of prior art vertical and flip chipmounted LED packages and thermal schematics where the optical emissionis substantially in the opposite direction of the heat removal.

FIGS. 2A, 2B and 2C depict side views of self-cooling solid state lightsources using luminescent thermally conductive luminescent elements andinterconnects with thermal schematics of the present invention.

FIGS. 3A, 3B and 3C depict side views of a self-cooling solid statelight source with multiple die of the present invention.

FIGS. 4A, 4B and 4C depict side views of printed electricalinterconnects on luminescent thermally conductive elements for variousLED die types of the present invention.

FIGS. 5A, 5B, 5C and 5D depict side views of various shapes ofwavelength conversion elements of the present invention.

FIGS. 6A and 6B depict a side view of two different mountings for LEDson wavelength conversion elements of the present invention.

FIGS. 7A, 7B and 7C depict side views of printed interconnects on LEDdie of the present invention.

FIGS. 8A, 8B, 8C and 8D depict side views of various environmental sealsfor self cooling light sources of the present invention.

FIGS. 9A and 9B depict side views of die shaping for enhanced dual sidedextraction of the present invention.

FIGS. 10A and 10B depict a side view and a graph of blue and red die inwavelength conversion elements of the present invention.

FIG. 11 depicts a top view of a three pin self cooling light source ofthe present invention.

FIG. 12 depicts a top view of a self cooling light source with anintegrated driver of the present invention.

FIGS. 13A and 13B depict a side view and a perspective view of a selfcooling light source with additional cooling means of the presentinvention.

FIG. 14 depicts a top view of a self cooling light source with thermallyisolated sections of the present invention.

FIG. 15 depicts a top view of a self cooling light source with separatedrive scheme for blue and red die of the present invention.

FIGS. 16A and 16B depict graphs of subtractive red phosphor and additivered LED of the present invention.

FIG. 17 depicts a graph of the spectrum from a self cooling light sourcewith cyan and yellow LEDs of the present invention.

FIGS. 18A and 18B depict a side view and a perspective view of variousshapes with luminescent coatings of the present invention.

FIGS. 19A and 19B depict side views of optics for self cooling lightsource of the present invention.

FIGS. 20A, 20B, and 20C depict side views of means of modifying the farfield optical patterns of self cooling light sources of the presentinvention.

FIGS. 21A, 21B, and 21C depict side views of a light emitting patchsource and its use with waveguiding materials of the present invention.

DETAILED DESCRIPTION OF DRAWINGS

FIG. 1A depicts a prior art vertical LED die 3 mounted on a substrate 4.The vertical LED die 3 is typically coated with an inorganic/organicmatrix 7 consisting of phosphor powder such as, but not limited to,Ce:YAG in a silicone resin material. The wire bond 2 is used toelectrically connect vertical LED die 3 to interconnect 5, which is thencoated with the inorganic/organic matrix 7. The other side of verticalLED die 3 is contacting interconnect 6 usually via eutectic solder orconductive adhesives. A lens 1 is further attached to substrate 4 toenvironmentally seal the assembly, enhance light extraction fromvertical LED die 3, and modify the far field optical pattern of thelight emitted by the device. In this case, emitted rays 9 aresubstantially traveling in the opposite direction of the heat ray 8.

As shown in the thermal schematic in FIG. 1A, cooling of theinorganic/organic matrix 7 occurs almost exclusively via thermalconduction through the vertical LED die 3 and into the substrate 4 viainterconnect 6. The heat generated within inorganic/organic matrix 7 dueto Stokes losses and scattering absorption is thermally conducted to thevertical LED die 3 at a rate determined by the thermal resistancedetermined by the bulk thermal conductivity of the inorganic/organicmatrix 7. As shown in the simplified thermal schematic, the averagetemperature of the inorganic/organic matrix 7 is determined by thethermal resistance R (phosphor/encapsulant) and T2 the averagetemperature of the vertical LED die 3. In order for heat generatedwithin the inorganic/organic matrix 7 to be dissipated to the ambient,it must move the thermal resistance of LED die 3 (RLED) and substrate 4(RPackage) before it can be dissipated to the ambient. This is asimplified thermal schematic, which lumps bulk and interface thermalresistances and spatial variations within the device. But in general,heat generated within the inorganic/organic matrix 7 must be dissipatedmainly through the vertical LED die 3 due to low thermal conductivity ofthe other materials (e.g. Lens) which surround inorganic/organic matrix7. Additional heatsinking means can further increase the surface areausing metal, composite, or ceramic elements to enhance the dissipationof heat to ambient but the flow of heat is still basically the same. Thelens 1 acts as an extraction element for the emitted light rays 9 butalso acts as a barrier to thermal rays 8. Typically constructed ofsilicone or epoxy resins with thermal conductivity less than 0.1 W/m/K,Lens 1 acts as a thermal insulator. Lens 1 also can limit thermalradiation from vertical LED 3 and inorganic/organic matrix 7 due to lowemissivity. In general this design requires that approximate 50% of theisotropic emission from the active region within vertical LED 1 must bereflected off some surface within the device and that the far fieldoutput of the device be substantially directional or lambertian innature. Even with the use of highly reflective layers, this represents aloss mechanism for this approach. These extra losses are associated withthe added pathlength that the optical rays must go through and multiplereflections off the back electrodes. This added pathlength andreflections, which are required to extract the light generated in theactive region of vertical LED 1, fundamentally reduces the efficiency ofthe LED based on the absorption losses of the LED itself. A significantportion of the light generated within the inorganic/organic matrix 7must also pass through and be reflected by vertical LED 1. Sincevertical LED 1 is not a lossless reflector, the added pathlength ofthese optical rays also reduce overall efficiency.

FIG. 1B depicts a prior art flipchip mounted LED 15. Solder orthermocompression bonding attaches flipchip mounted LED 15 via contacts16 and 21 to interconnects 17 and 18 respectively on substrate 19.Luminescent converter 14 may be an inorganic/organic matrix as discussedin FIG. 1A or solid luminescent element such as a Ce:YAG ceramic, singlecrystalline Ce:YAG, polycrystalline Ce:YAG or other solid luminescentmaterials as known in the art. In either case, the same coolingdeficiency applies with this design. Virtually all the cooling of theluminescent converter 14 must be through the flipchip mounted LED 15.Again, emission rays 12 travel in a direction substantially opposite tothermal rays 13 and once again approximately 50% the isotropic emissionof the active region of the flipchip mounted LED 15 must to redirectedwithin the device requiring the use of expensive metals like Ag,specialized coating methods and even nanolithography as in the case ofphotonic crystals.

The formation of contacts which are both highly reflective over a largeportion of the LED die area and still forms a low resistivity contacthas been a major challenge for the industry due to reflectivitydegradation of Ag at the temperature typically required to form a goodohmic contact. This high light reflectivity and low electricalresistivity leads to added expense and efficiency losses. Because boththe contacts must be done from one side typically an underfill 20 isused to fill in the voids created by the use of flipchip contacts. Lens11 again forms a barrier to heat flow out of the device from bothconvectively and radiatively. The luminescent converter 14 is typicallyattached after the flipchip mounted die 15 is mounted and interconnectedto substrate 19. A bonding layer 23 between the flipchip mounted die 15and luminescent element 14 further thermally isolates the luminescentelement 14. Typically, InGaN power LED UV/Blue chips exhibitefficiencies approaching 60% while White InGaN power LED packages aretypically 40%. The loss within the luminescent converter 14 thereforerepresents a substantial portion of the total losses within the device.In the case of an inorganic/organic matrix luminescent converter of FIG.1A, the conversion losses are further localized within the individualphosphor powders due to the low thermal conductivity of the silicone orepoxy matrix. The solid luminescent converter 14 has more lateralspreading due to the higher thermal conductivity of the solid material.Both cases are typically Cerium doped YAG with an intrinsic thermalconductivity of 14 W/m/K. However since the silicone matrix has athermal conductivity less than 0.1 W/m/K and surrounds substantially allthe phosphor powders, the inorganic/organic matrix has a macro thermalconductivity roughly equivalent to the silicone or epoxy by itself. Veryhigh loading levels of phosphor powder can be used but lead toefficiency losses due to higher scatter.

There is simply nowhere for the heat generated in luminescent converter14 to go except be thermally conducted into the flipchip mounted LED 15via the bonding layer 23. In most cases, solid luminescent converters 14must have an additional leakage coating 22 that deals with blue lightthat leaks out of the edge of the flipchip mounted LED 15. Aninorganic/organic matrix suffers from the same issues in FIG. 1A. Inboth FIGS. 1A and 1B, the emission surface are substantially differentfrom the cooling surfaces. The thermal schematic for FIG. 1B is similarto FIG. 1A in that heat generated within the luminescent converter 14 issubstantially dissipated through the flipchip mounted LED 15. With theadvent of high powered LEDs, a substantially portion of the heatgenerated within the device can be localized within luminescentconverter 14. This localization has led to a variety of solutionsincluding the use of remote phosphors. In general, luminescent converter14 efficiency reduces as its average temperature T4 increases. In theprior art the luminescent converter 14 dissipates the majority of itsheat through the flipchip mounted LED 15 with an average temperature ofT5. This is an inherently higher temperature than the ambient. The needexists for techniques whereby the heat generated within luminescentconverter 14 can be reduced for higher efficiency devices.

FIG. 2A depicts a vertical LED 24 of the present invention in which theoptical emission rays 26 travel substantially in the same direction asthe thermal rays 27. A thermally conductive luminescent element 25provides wavelength conversion for at least a portion of the lightemitted by vertical LED 24 and acts as an optical and thermal spreadingelement, extraction means, and a substrate for the electricalinterconnect. In FIG. 2A, overcoat 30 may be reflective, transparent,partially reflective and exhibit reflectivity which is wavelength and/orpolarization dependent.

Wire bond 29 connects interconnect 28 to contact pad 33 with contact 34attached via conductive ink or eutectic solder to interconnect 31. Atransparent/translucent bonding layer 32 maximizes optical and thermalcoupling into thermally conductive luminescent element 25 and eventuallyout of the device. The transparent/translucent bonding layer 32 mayconsist of, but is not limited to, glass frit, polysiloxane,polysilazane, silicone, and other transparent/translucent adhesivematerials. Transparent/translucent bonding layer 32 has a thermalconductivity greater than 0.1 W/m/K and even more preferably greaterthan 1 W/m/K. Thermally conductive luminescent element 25 may consistof, but is not limited to, single crystal luminescent materials,polycrystalline luminescent materials, amorphous luminescent materials,thermally conductive transparent/translucent materials such as Sapphire,TPA, Nitrides, Spinel, cubic zirconia, quartz, and glass coated with athermally conductive luminescent coating, and composites of thermallyconductive transparent/translucent material and thermally conductiveluminescent materials.

In FIG. 2A a high emissivity layer 35 may be applied to the thermallyconductive luminescent element 25 to enhance radiative cooling. Inaddition, high emissivity layer 35 may also provide enhanced extractionefficiency by acting as an index matching layer between the surroundingair and the thermally conductive luminescent element 25, especially inthe case where extraction elements are used to increase extraction fromthe thermally conductive luminescent element 25. Unlike the previousprior art thermal schematic, the flow of heat generated in the thermallyconductive luminescent element 25 is directly coupled to the ambient viaconvective and radiative cooling off the surface of the thermallyconductive luminescent element 25 itself. This direct coupling approachcan only be effectively accomplished if the bulk thermal conductivity ofthe thermally conductive luminescent element 25 is high enough toeffectively spread the heat out over an area sufficiently large enoughto effective transfer the heat to the surrounding ambient. As such, athermally conductive luminescent element has a surface area greater thanthe attached LED with an average bulk thermal conductivity greater than1 W/m/K wherein the heat generated within the Vertical LED 24 andthermally conductive luminescent element 25 are substantiallytransferred to the surrounding ambient via convection and radiation offthe surface of thermally conductive luminescent element 25. Highemissivity layer 35 most preferably has an emissivity greater than 0.8at 100 degrees C. and an absorption less than 0.2 throughout the visiblespectrum. Alternately, the emissivity of the thermally conductiveluminescent element 25 may be greater than 0.8 at 100 degrees C. andhave an absorption less than 0.2 throughout the visible spectrum.

FIG. 2B depicts a flip chip mounted LED 36 mounted on thermallyconductive luminescent element 42 via a transparent/translucent bondinglayer 43 and electrically connected via contacts 41 and 40 tointerconnects 44 and 45 on thermally conductive luminescent element 25.Interconnects 44 and 45 are thick film silver conductors formed viascreen printing, inkjet printing, lithographic means, or combinations ofthese other methods. As an example, thermally conductive luminescentelement 42 may contain a laser cut trench approximately 5 micron deepinto which silver paste is screen printed and fired. The surface ofconductive luminescent element 42 is then optionally lapped to create asmooth surface for interconnect 44 and 45. The resulting surface is nowsmooth enough for thermo compression bonded die, direct die attach diewith integral eutectic solders, and other direct attach bonding methods.The interconnects 44 and 45 are typically fired at a temperature greaterthan 400 degrees C. The interconnects 44 and 45 are thick film or inkjetsilver traces with line widths less than or greater than the width ofthe flip chip mounted LED 36. Optical losses within the device can beminimized by minimizing the amount of silver used, minimizing the widthof the interconnect traces and maximizing the reflectivity of the silvertraces. Alternately, the thermal resistance between flipchip mounted LED36 and the thermally conductive luminescent element 42 may be minimizedby increasing the amount of silver thickness or area. Overcoat 37 mayconsist of, but is not limited to, glass frit, polysiloxane,polysilazanes, flame sprayed ceramics, and evaporative/CVD coatings. Ahighly reflective layer in overcoat 37 is optional. In this manner, acompact directional light source can be formed. Transparent/translucentbonding layer acts as an environmental and shorting barrier for thedevice. The reflector in overcoat 37 can be applied after all the hightemperature processing thereby maximizing reflectivity of the layer. Thethermal schematic shown in FIG. 2B again shows that there is a muchdifferent thermal conduction path than FIG. 1 devices. Thermallyconductive luminescent element 42 provides the cooling surfaces for thedevice as well as conversion of light from LED 36. The emitting surfaceof the device is also the cooling surface of the device.

FIG. 2C depicts a lateral LED 53 mounted onto thermally conductiveluminescent element 46. As in FIG. 2A and FIG. 2B, the optical emission50 and thermal rays 51 travel in substantially the same direction. Inthis configuration, a transparent/translucent overcoat 48 couplesthermal rays 56 and optical emission 57 out the backside of the device.Optical emission 50 and optical emission 57 maybe the same or differentfrom each other regarding emission spectrum, intensity, or polarization.Additives, coatings, and combinations of both can effect the emissionspectrum, intensity and polarization within overcoat 48. Interconnect 49and 54 may consist of, but are not limited to, electrically conductivematerials in a dielectric matrix. A silver flake thick film paste screencan be printed and fired at greater than 400 degrees C. with areflectivity greater than 50% to form an electrically conductivematerial in a dielectric matrix. Wire bond 47 and 52 connect LEDcontacts 56 and 55 to interconnect 49 and 54 respectively. Gold wire ispreferred but the wire bond can be silver, silver coated gold, andaluminum in wire, foil, and tape form. The thermal schematic illustratesthe flow of heat through the device to ambient. Transparent/translucentovercoat 48 may also contain luminescent materials. As an example,transparent/translucent overcoat 48 may consist of inorganic/organicmatrix material such as but not limited to HT 1500 Polysilazane(Clariant Inc.) containing at least one luminescent materials such as,but not limited to, Eljen EJ-284 fluorescent dye for conversion of greenand yellow emission into red. Luminescent coatings can be applied viadip coating, spraying, inkjet, and other deposition techniques to formtransparent/translucent overcoat 48 on a light emitting devicecontaining at least one thermally conductive luminescent element 46.

FIG. 3A depicts a self cooling light source consisting of a singlethermally conductive luminescent element 60 attached both thermally andoptically onto at least one LED 61. LED 61 may consist of InGaN, GaN,AlGaN, AlinGaP, ZnO, Al, and diamond based light emitting diodes. Bothblue and red light emitting diodes such as, but not limited to, InGaNand AlinGaP LEDs are attached optically and thermally to at least onethermally conductive luminescent element 60. Heat 59 and emission 58generated by the LED 61 and the thermally conductive luminescent element60 are spread out over a substantially larger area and volume than theLED 61. In this manner the heat generated can be effectively transferredto the surrounding ambient.

Ce:YAG in single crystal, polycrystalline, ceramic, and flame sprayedforms are preferred materials choices for thermally conductiveluminescent element 60. Various alloys and dopants may also be usedconsisting of but not limited to gadolinium, gallium, and terbium. Thethermally conductive luminescent element 60 can be single crystal ceriumdoped YAG grown via EFG with a cerium dopant concentration between 0.02%and 2%, preferably between 0.02% and 0.2% with a thickness greater than500 microns. Alternatively, the thermally conductive luminescent element60 can be flamesprayed Ce:YAG with an optional post annealing. Thethermally conductive luminescent element 60 can be formed by flamespraying, HVOF, plasma spraying under a controlled atmosphere directlyonto the LED 61. This approach maximizes both thermal and opticalcoupling between the thermally conductive luminescent element and LED 61by directly bonding to LED 61 rather than using an intermediary materialto bond the LED 61 to thermally conductive luminescent element 60.Alternately, the thermally conductive luminescent element 60 maybeformed using at least one of the following methods; hot pressing, vacuumsintering, atmospheric sintering, spark plasma sintering, flamespraying, plasma spraying, hot isostatic pressing, cold isostaticpressing, forge sintering, laser fusion, plasma fusion, and other meltbased processes. Thermally conductive luminescent element 60 may besingle crystal, polycrystalline, amorphous, ceramic, or a meltedcomposite of inorganics. As an example, 100 grams alumina and Ce dopedYag powder which have been mixed together are placed into a container.The powders are melted together using a 2 Kw fiber laser to form amolten ball within the volume of the powder. In this manner the powderacts as the crucible for the molten ball eliminating any contaminationfrom the container walls. The use of the fiber laser allows forformation of the melt in approximately 4 seconds depending on the beamsize. While still in a molten state the ball may optionally be forgedbetween SiC platens into a plate. Most preferably the molten ball isgreater than 10 mm in diameter to allow sufficient working time as amolten material for secondary processing. The plate may be furtherprocessed using vacuum sintering, atmospheric sintering, or hotisostatic pressing to form a translucent thermally conductiveluminescent element 60. The use of fiber laser based melt processing isa preferred method for the formation of luminescent oxides, nitrides,and oxynitrides as a method of reducing energy costs compared to hotpressing or vacuum sintering. The use of controlled atmospheresincluding vacuum, oxygen, hydrogen, argon, nitrogen, and ammonia duringthe laser based melting processes is disclosed. While fiber lasers arepreferred the use of localized actinic radiation to form a molten masswithin a powder mass to form thermally conductive luminescent element 60is disclosed.

FIG. 3B depicts a self cooling light source consisting of at least twothermally conductive luminescent elements 62 and 63 attached to at leastone LED 64. In this case, both thermal emission 64 and optical emission65 can be spread out and extracted from both sides of LED 64. In allcases, multiple LEDs allow for parallel, series, anti-parallel, andcombinations of all three with the appropriate electrical interconnect.In this case, optical emission 65 can be substantially similar ordifferent on the two sides of the devices. As an example, thermallyconductive luminescent element 62 can be 1 mm thick single crystal Cedoped YAG formed via EFG boule, which is then sliced into 19 mm×6 mmwafers. The sliced surface enhances extraction of the Ce:YAG emissionout of the high index of refraction Ce:YAG material. Alternately,thermally conductive luminescent element 63 may be a pressed andsintered translucent polycrystalline alumina with a thermally fusedlayer of Mn doped Strontium Thiogallate and a layer of Eu dopedStrontium Calcium Sulfide within a glass frit matrix. In this manner, awide range of optical emission spectrums can be created.

In this particular case, the two sides of the devices will emit slightlydifferent spectrums. In general, unless an opaque reflector is placedbetween thermally conductive luminescent elements 62 and 63 there willbe significant spectral mixing within this device. This configurationcan be used for quarter lights, wall washers, chandeliers, and otherlight fixtures in which a substantial portion of the optical emission 65is required to occur in two separate directions. Directional elementssuch as BEF, microoptics, subwavelength elements, and photonicstructures impart more or less directionality to the optical emission 65of either thermal conductive luminescent elements 62 and/or 63.

In another example, Cerium doped YAG is formed via flame, HVOF, orplasma spraying and then optionally annealed, spark plasma sintered,microwave sintering, or HIP to improve its luminescent properties forone or both thermally conductive luminescent element 62 and/or 63. Atleast one InGaN LED and at least one AlInGaP LEDs are used for at leastone LED 64.

In yet another example, high purity aluminum oxide is flamesprayeddirectly onto at least one LED die 64 for thermally conductiveluminescent element 62 forming a translucent reflector. The emissivityof flame sprayed aluminum oxide is typically 0.8 allowing for enhancedradiative cooling from that surface. Thermally conductive luminescentelement 63 is single crystal Ce:YAG formed via skull melting and slicedinto 0.7 mm thick wafers 0.5 inch×1 inch in area with a cerium dopingconcentration between 0.1% and 2%. In this case thermally conductiveluminescent element 62 does not necessarily contain a luminescentmaterial but acts as diffuse reflector and thermal spreading element forthe heat generated by both LED 64 and thermally conductive luminescentelement 62. By embedding LED 64 directly into thermally conductiveluminescent element 62 it is possible to eliminate pick and place, dieattachment processes and materials, and maximize both thermal transfer64 and optical emission 65 by eliminating unnecessary interfaces.Additional luminescent materials and opaque reflectors can be positionedwithin or coating onto either thermally conductive luminescent elements62 or 63. Pockets or embedded die can recess the die such that printingtechniques including but not limited to inkjet, silkscreen printing,syringe dispensing, and lithographic means.

FIG. 3C depicts two thermally conductive luminescent elements 72 and 74providing thermal conduction paths 74 and 79 to additional cooling means71 and 73. In this case, thermally conductive luminescent elements 72and 74 allow for thermal emission 76 and optical emission 77 and alsoprovide for thermal conduction paths 74 and 79. Additional cooling means71 and 73 may also provide for electrical connection to LED 75 viainterconnect means previously disclosed in FIG. 2. One or moreadditional cooling means 71 and 73 further enhance the amount of heatthat can be dissipated by the device. As an example, a typical naturalconvection coefficient is 20 W/m2/K and CeYag has an emissivity of 0.8near room temperature. A self cooling light source consisting of two ¼inch×½ inch×1 mm thick pieces of CeYag 72 and 74 with four direct attachLEDs 75 soldered on silver thick film interconnect traces has a surfacearea of approximately 2.3 cm2. Using natural convection and radiativecooling approximately 500 milliwatts of heat can be dissipated off thesurface of the self cooling light source if the surface temperature isapproximately 100 degrees C. and the ambient is 25 degrees C. and theemissivity is 0.8. Of the 500 milliwatts, 350 milliwatts of heat isdissipated via natural convection cooling and 150 milliwatts aredissipated via radiation. A typical 4000K spectrum output has an opticalefficiency of 300 lumens per optical watt. If the solid state lightsource has a electrical to optical conversion efficiency of 50%, 500milliwatts of optical output is generated for every 500 milliwatts ofheat generated. Under these conditions a ¼ inch×½ inch solid state lightsource operating with a surface temperature of approximately 100 degreesC. can output 150 lumens without the need for additional heatsinkingmeans. The use of additional cooling means 71 and 73 can be used tosignificantly increase this output level by increase the surface areathat heat can be convectively and radiatively transferred to theambient. As is easily seen in the example, increasing the surface areais directly proportional to amount of heat that can be dissipated. It isalso clear that the electrical to optical conversion efficiencydramatically affects the amount of heat generated, which a key attributeof this invention. Unlike conventional LED packages light generatedwithin this self cooling solid state light source is extracted out ofboth sides of the device. Isotropic extraction as shown has a 20%theoretical higher efficiency than lambertian extraction. Also usingthis approach, the temperature difference between the LED 75 junctionand the surfaces of thermally conductive luminescent elements 72 and 74can be very low if the thermal conductivity is greater than 10 W/m/K andthe LEDs 75 are attached such that there is low thermal resistance tothe surrounding thermally conductive luminescent elements 72 and 74. Inaddition, cooling means 71 and 73 may be physically different to allowfor the device to connect to different external power sources correctly.As an example, cooling mean 71 may be a pin and cooling means 73 maybe asocket such that a keyed electrical interconnect is formed. Alternately,cooling means 71 and 73 may contain magnets, which allow for attachmentof external power sources. Even more preferably the magnets havedifferent polarity such that a keyed interconnect can be formed.Additional cooling means 71 and 73 may include, but are not limited to,heatpipes, metals, glass, ceramics, boron nitride fibers, carbon fibers,pyrolytic graphite films, and thermally conductive composities. As anexample, boron nitride nano tubes fibers, as provided by BNNT Inc., arepressed with exfoliated boron nitride flakes to form and thermallyinterconnected skeleton matrix using pressing, cold isostatic pressing,warm isostatic pressing, and/or hot isostatic pressing to form a solidsheet. The boron nitride nanotube fibers interconnect the boron nitrideflakes and bond to the surface of the boron nitride flakes such that acontinuous thermal matrix is formed. The resultant skeleton matrix maythen be infused with polymeric or polymeric ceramic precursors includingbut not limited to polysilazane, polysiloxane, glasses, silicones, andother polymeric materials to form a composite. Alternatively, The boronnitride nano tube fibers may be formed into a yarn and woven into acloth or felt and then infused with to form a thermally conductivecomposite. Alternately, high thermal conductivity carbon fibers andfilms may be used but boron nitride is preferred due to its low opticalabsorption compared to carbon based approaches. Alternately, carbonbased additional cooling means 71 and 73 may include a reflective layerto reduced absorption losses and redirect light from the source as wellas provide additional cooling. Additional cooling means 71 and 73 mayalso diffuse, reflect, or absorb optical emission 77 emitting between orfrom the adjacent edge of thermally conductive luminescent element 72 or74. In this manner the far field emission of the device can be adjustedboth from an intensity and spectral standpoint. Doubling the surfacecooling area using additional cooling means 71 and 73 approximatelydoubles the lumen output as long as the thermal resistance of theadditional cooling means 71 and 73 is low.

FIG. 4A depicts at least one LED 85 embedded within thermally conductiveluminescent element 83. Thermally conductive luminescent element 83 maybe formed via press sintering of aluminum oxide as known in the art toform a translucent polycrystalline alumina TPA with depressionssufficiently deep enough to allow for LED 85 to be recessed. Luminescentcoating 84 may be substantially only in the pocket formed in thermallyconductive luminescent element 83 or may cover substantially all thesurfaces of thermally conductive luminescent element 83. Alternately,single crystal, polycrystalline or amorphous phosphor, pieces, plates,rods and particles can be fused or bonded into or onto thermallyconductive luminescent element 83. In this manner, the quantity ofluminescent material can be minimized while maintaining high thermalconductivity for the thermally conductive luminescent element 81.

As an example, single crystal Ce:YAG pieces 1 mm×1 mm and 300 micronsthick can be fusion bonded into 1.1 mm×1.1 mm×500 micron deep pocketsformed into TPA press sintered plates and then fired at 1700 degrees C.in a vacuum for 10 hours such that the single crystal YAG pieces areoptical and thermally fused into the bottom of the TPA pockets. LED 85can then be bonded into the remaining depth of pocket and be used toexcite the single crystal Ce:YAG pieces locally. The combined opticalemission from LED 85 and the single crystal Ce:YAG pieces would bespread out and extracted by the sinter pressed TPA while stillmaintaining high thermal conductivity.

Alternately, luminescent powders in glass frits, polysiloxane,polysilazane, and other transparent binders can form luminescent coating84. In particular, high temperature binders in luminescent coating 84such as polysilazane with luminescent powders, flakes, rods, fibers andin combination both pre-cured and as a bonding agent can be positionedbetween thermally conductive luminescent element 83 and at least one LED85.

Materials with high visible spectrum transmission, lower refractiveindex, high thermal conductivity, and low processing costs for net andfinal shape are preferred materials for thermally conductive luminescentelement 83. These materials include, but are not limited to, TPA,Spinel, Quartz, Glass, ZnS, ZnSe, ZnO, MgO, AlON, ALN, BN, Diamond, andCubic Zirconia. In particular, Spinel and TPA formed via press sinteringare low cost of manufacture of net shape parts. The use of techniquesused to form TPA parts as seen in transparent dental braces as known inthe art with luminescent elements either as coatings or bonded elementscan create thermally conductive luminescent element 83.

With LED 85 recessed into thermally conductive luminescent element 83,printing and lithographic methods can be used to electricallyinterconnect at least one LED 83 to outside power sources and/or otherLEDs or devices. Unlike wirebonding, this approach creates a low profilemethod of interconnecting LEDs, which eases assembly of multiple sticksand reduces costs.

In one example, LED 85 is bonded into a pocket formed via laser ablationin a 1 mm thick wafer of Spinel to form thermally conductive luminescentelement 83. In this example the Spinel may or may not includeluminescent elements or properties. The majority of the wavelengthconversion instead occurs locally around LED 85 via luminescent coating84 and/or additional luminescent coating 82. This minimizes the amountof luminescent material necessary yet still allows for a low thermalresistance to ambient for the luminescent materials. While only a singleside is shown in FIG. 4, the light source may also be bonded to anotherlight source, heatsink, another transparent/translucent thermallyconductive element to further enhance cooling and optical distributionfrom LED 85 and any luminescent elements within the light source. LED 85is bonded into the pocket using polysilazane containing 0.1% to 2% dopedCe:YAG powder with a particle size below 10 microns.

Transparent/translucent dielectric layer 81 is inkjet printed over atleast one LED 85 except contact pads 87 and 86. In the case where LED 85uses TCO based contacts, at least a portion of the TCO is not covered bytransparent/translucent dielectric 81 to allow for electrical contact.Optionally an additional luminescent coating 82 may be printed or formedon at least one LED 85 to allow for additional wavelength conversion andto create a more uniform spectral distribution from the device.Interconnects 80 and 88 may then be applied either before or aftercuring of transparent/translucent dielectric 81. Polysilazane,polysiloxane, glass frit, spin-on glasses, and organic coatings areexamples of transparent/translucent dielectric 81, preferably thecoatings can maintain transparency above 300 degrees C. Formulationscontaining Polysilazane with and without luminescent elements arepreferred materials for additional luminescent coating 82,transparent/translucent dielectric 82 and luminescent coating 84.Preferred luminescent elements are powder phosphors, quantum dots,fluorescent dyes (example wavelength shifting dyes from EljenTechnologies) and luminescent flakes and fibers.

Electrical connection to LED 85 is via interconnects 80 and 88 forlateral LED designs. Precision inkjet printing of silver conductive inksand/or screen printing of thick film silver inks form interconnects 80and 88. As an example thick film silver paste is screen printed andfired onto thermally conductive luminescent element 83 up to the pocketfor LED 85. Transparent/translucent dielectric 81 is inkjet printed suchthat only contacts 87 and 86 are left exposed and thetransparent/translucent dielectric 81 covers the rest of the exposedsurface of LED 85 and at least a portion of thermally conductiveluminescent element 83 in a manner to prevent shorting out LED 85 butstill allowing access to the thick film silver paste conductors appliedearlier. After or before curing of transparent/translucent dielectric 81and optionally additional luminescent coating 82, conductive ink isinkjet printed connecting the thick film silver conductor appliedpreviously to the contacts 86 and 87. Using this approach, alignmentissues can be overcome due to the availability of inkjet systems withimage recognition and alignment features while still allowing for lowresistance conductors. In general, while inkjet printing of conductorscan be very accurate and be printed with line widths under 50 microns,the thickness is typically limited to under 10 microns which limits thecurrent carry capacity of long lines. Using this approach, thick filmsilver conductors which can be over 50 microns thick can be used tocarry the majority of the current and then short inkjet printed tracescan be used to stitch connect between the thick film silver conductorsand contacts 87 and 86. Using this approach, gold wire bonding can beeliminated.

A transparent/translucent overcoat 89 may be applied over at least aportion of interconnects 80 and 89 and/or transparent/translucentdielectric 81, additional luminescent coating 82, and thermallyconductive luminescent element 83 to environmentally and/or electricallyisolate the device. Protective barrier layers on LED die 85 can beformed during LED fabrication to facilitate or even eliminate the needfor transparent/translucent dielectric layer 81 and allow for directprinting of interconnect 89 and 88 onto contacts 87 and 86 respectively.Catalytic inks and/or immersion plating techniques allow for theformation of thicker/lower resistivity traces for interconnect 89 and88, eliminate the need for thick film printing and allow for the use ofinkjet printing for the entire interconnect. Preferred materials fortransparent/translucent overcoat 89 include but are not limited topolysilazane, polysiloxane, spin-on glasses, organics, glass frits, andflame, plasma, HVOF coatings. Planarization techniques based on spin-onglasses and/or CMP can be used for transparent/translucent overcoat 89.Luminescent elements including but not limited to powders, flakes,fibers, and quantum dots can be incorporated in transparent/translucentovercoat 89, transparent/translucent dielectric 81, and additionalluminescent coating 82. Luminescent elements may be spatially oruniformly dispersed in these layers.

FIG. 4B depicts a light source in which a luminescent layer 91 is formedon a transparent/translucent element 90 containing extraction elements.Transparent/translucent element 90 can be, but is not limited to, singlecrystalline materials such as sapphire, cubic zirconia, YAG (doped andundoped), ZnO, TAG (doped and undoped), quartz, GGG (doped and undoped),GaN (doped and undoped), AlN, oxynitrides (doped and undoped),orthosilicates (doped and undoped), ZnS (doped and undoped), ZnSe (dopedand undoped), and YAGG (doped and undoped), polycrystalline materials,and amorphous materials such as glass, ceramic YAG (doped and undoped),ALON, Spinel, and TPA. In general, single crystal materials grown viaverneuil, EFG, HEM, Czochralski, CVD, hydrothermal, skull, and epitaxialmeans can be the transparent/translucent element 90.

Luminescent layer 91 may be formed directly one transparent/translucentelement 90 or be formed separately and then bonded totransparent/translucent element 90. Flamespraying, plasma spraying, andHVOF techniques can form either or both luminescent layer 91 andtransparent/translucent element 90. The light source can have atransparent/translucent element 90 with an alpha less than 10 cm-1throughout the visible spectrum and a luminescent layer 91 containing atleast one luminescent element emitting between 400 nm and 1200 nm. Theluminescent layer 91 can exhibit a refractive index, which is not morethan 0.2 different than transparent/translucent element 90. LED 99 maybe InGaN, AlInGaP, ZnO, BN, Diamond, or combinations of InGaN, AlInGaP,ZnO, BN, or diamond.

Both InGaN and AlInGaP LEDs can be used for LED 99 combined with atransparent/translucent element 90 consisting of at least one of thefollowing materials; sapphire, Spinel, quartz, cubic zirconia, ALON,YAG, GGG, TPA, or ZnO and luminescent layer 91 and/or additionalluminescent layer 98 containing Ce doped YAG. An additional red phosphoremitting between 585 and 680 nm can be used within luminescent layer 91and/or additional luminescent layer 98. These elements form a selfcooling light source which emits an average color temperature between6500K and 1200K that lies substantially on the black body curve is apreferred embodiment of this invention. The self cooling light sourcecan emit an average color temperature between 4000K and 2000K than liessubstantially on the blackbody curve.

Multiple self cooling light sources can be used within a fixture,reflector, optic or luminaire such that color and intensity variationsare averaged out in the far field. Three or more self cooling lightsources within a fixture, reflector, optic or luminaire creates auniform illumination at a distance greater than 6 inches from thesources. Transparent/translucent dielectric layer 93 may be inkjetprinted, silk screen printed, formed via lithographic means and exhibitsan alpha less than 10 cm-1 throughout the visible spectrum. Interconnect95 and 94 may be printed using inkjet, silkscreen, template, orlithographic means. Catalytic inks and immersion plating techniquesincrease conductor thickness and thereby reduce resistivity. Silvertraces with a trace width less than 500 microns and a reflectivitygreater than 50% for interconnect 95 and 94 reduce absorption of thelight generated within the light source. Contacts 96 and 97 on LED 99may be on one side only as in lateral devices or consist of one topcontact and one side contact as previously disclosed in US PatentApplication 20060284190, commonly assigned and herein incorporated byreference.

FIG. 4C depicts a self-cooling light source with at least one verticalLED 100 mounted to or at least partially embedded in thermallyconductive luminescent element 103. Composite, layer, single crystal,polycrystalline, amorphous, and combinations as described previously canbe used for the thermally conductive luminescent element 103. In thisparticular example, one vertical LED 100 is mounted such thatinterconnect 101 and 102 may be printed via inkjet, silkscreening, orlithographic means directly on thermally conductive luminescent element103 and in contact with a side of vertical LED 100. This embodimenteliminates the need for an additional dielectric and allows for the useof vertical LED devices, which inherently exhibit lower Vf than lateraldevices. A substrate free LED as described in US patent application20090140279 (commonly assigned and incorporated herein by reference) isa preferred embodiment for LED 100. Direct die attach and flip chipmounting configurations may also be used for LED 100. For the substratefree case, InGaN and/or AlinGaP vertical LED 100 has TCO contacts 104and 105 for LED 100 wherein the interconnects 101 and 102 are thick filmsilver inks which form ohmic contact to the adjacent TCO contact 104 and105. In this manner, absorption losses are minimized and the need forlithographic steps to fabricate LED 100 is eliminated or minimized. Aself cooling light source contains at least one vertical LED 100 withTCO contacts 104 and 105 connected via thick film silver traces forinterconnect 101 and 102 directly bonded to TCO contacts 104 and 105 ona thermally conductive luminescent element 103. Optionally, bondinglayer 106 may be used to mount, improve extraction, incorporateadditional luminescent materials or position LED 100 onto or withinthermally conductive luminescent element 103.

FIG. 5 depicts various shapes of thermally conductive luminescentelements. FIG. 5A depicts a substantially flat luminescent element 107.Thickness is a function of dopant concentration but typically thethickness ranges from 200 micron to 2 mm for a uniformly doped Ce dopedYAG with a Cerium doping concentration between 0.02% and 10%. In orderfor efficient thermal spreading to occur, the thermal conductivity ofthe thermally conductive luminescent element 107 needs to be greaterthan 1 W/m/K to adequately handle average power densities greater than0.1 W/cm2 of surface area on luminescent element 107. If the thermalconductivity is to low there is insufficient thermal spreading of theheat generated within the device which decreases the ability of the flatluminescent element 107 to cool itself via natural convection andradiative means.

FIG. 5B depicts a non-flat (hemispheric) luminescent element 108. Inthis case, light extraction can be enhanced for those rays that arewaveguiding within the higher refractive index of non-flat luminescentelement 108. In addition, far field intensity and wavelengthdistributions can be modified. Multiple smaller self cooling lightsources with the same or different shaped thermally conductiveluminescent elements create uniform or specific far field intensity andwavelength distributions. The extraction of light generated within amedium with a refractive index greater than air is restricted by totalinternal reflection per Snell's Law. Shaped luminescent elements 108 canbe used to reduce the average optical path length of optical raysrequired to escape the luminescent element 108. Since absorption lossesare directly proportional to the optical path length for a givenabsorption coefficient (alpha), reducing the average optical path lengthdirectly translates into reduced absorption losses. The spatial locationof where the optical rays are generated within luminescent element 108,the refractive index of luminescent element 108, absorption coefficient(alpha) of luminescent element 108, bulk and surface scattering withinand on luminescent element 108, and the geometry of luminescent element108 can all be modeled as known in the art to optimize the extractionefficiency.

FIG. 5C depicts a non-flat (curved) thermally conductive luminescentelement 109 with a substantially uniform thickness. In this mannerextraction can be enhanced by maintaining a uniform thickness ofluminescent material. Extrusion, pressing, molding, sawing, boring, andflame spraying techniques as known in the art may be used to fabricatevarious shapes of thermally conductive luminescent elements.

FIG. 5D depicts a non-flat (rectangular saw tooth) thermally conductiveluminescent element 110 with additional surface elements to enhanceconvection cooling and optionally to modify or homogenize the emissionoutput of the self-cooling light source. Extrusion, pressing, andmolding techniques may be used to form thermally conductive luminescentelement 110.

FIG. 6A depicts a partially embedded LED 108 within a depression inthermally conductive luminescent element 107 mounted via bonding layer109. The formation of the depression may be by laser machining, ebeammachining, etching (both chemical and mechanical), plasma etching,molding, and machining means. Substrate-free LEDs may be used forpartially embedded LED 108 with a thickness less than 300 microns. Byembedding partially embedded LED 108 in thermally conductive wavelengthconversion element 107, the thermal resistance between the two elementscan be reduced which lowers the junction temperature of the LED for agiven drive level. Optionally, more of the emission from partiallyembedded LED into thermally conductive luminescent element 107 can becoupled thereby changing the color temperature of the self cooling lightsource.

FIG. 6B depicts at least one LED 112 bonded onto thermally conductiveluminescent element 110 via bonding layer 111. In this case, bondinglayer 111 should exhibit a thermal conductivity greater than 1 W/m/K andan alpha less than 10 cm-1 for the emission wavelengths of LED 112.

FIG. 7 depicts various printed contacts for TCO contact based LEDs. FIG.7A depicts a vertical LED consisting of a top silver paste contact 113on TCO layer 114 on p layer 117. Active region 116 is between p layer117 and n layer 115 with n layer 115 covered with TCO contact 118 andbottom silver paste contact 119. A substrate free LED allows dual sidedgrowth of TCO contact layers 114 and 118 on substrate free LEDstructures consisting of p layer 117, active layer 116 and n layer 115.Thick film high temperature silver paste contacts 113 and 119 can beprinted on LEDs with TCO contacts 114 and 118 and fired at temperaturesgreater than 200 degrees C. in various atmospheres to form a low opticalabsorption, low Vf, and substantially lithography free LED devices.

FIG. 7B depicts a lateral device with printed/inkjet printed contacts120 and 125. In all cases, ohmic contact to the n layer may include ornot include an intermediary TCO layer to form reasonable ohmic contact.In FIG. 7B, TCO 122 is grown on p layer 123. Active layer 124 is betweenp layer 123 and n layer 125. TCO 122 is doped ZnO grown via CVD with aresistivity less than 0.003 ohm-cm and greater than 1000 Angstromsthick. Printed etch masks allow for etch of the step down to n layer125. As an example, an AlInGaP LED epi may be grown on GaAs. The wafercan be etched and patterned to form the lateral device having TCO 122 onthe p layer 123. Printed contacts 120 and 125 are formed on TCO 122 andn layer 125. Optionally an additional TCO layer maybe formed of n layer125 to further reduce Vf. The addition of a eutectic solder layer toprinted contact 120 and 125 to create a direct die attach die is alsodisclosed. In a preferred embodiment, the AlinGaP epi is removed viachemical etching using a sacrificial etching layer between the AlinGaPand GaAs substrate as known in the art. The resulting direct attach diemay be additionally wafer bonded to GaN substrates as disclosed in U.S.Pat. Nos. 7,592,637, 7,727,790, 8,017,415, 8,158,983, and 8,163,582, andUS Patent Applications Publication Nos. 20090140279 and 20100038656,commonly assigned as the present application and herein incorporated byreference.

FIG. 7C depicts a printed contact with a top contact 126 and sidecontacts 132 and 130. Again TCO 127 forms a low ohmic transparent ohmiccontact to p layer 128 and the active region 129 is between p layer 128and n layer 130. Side contacts 131 and 132 contact the side walls of nlayer 130. N layer 130 is greater than 10 microns of thickness. Evenmore preferably, the thickness of n layer 130 is greater than 50 micronsbut less than 250 microns.

FIG. 8 depicts various methods of changing the far field distribution ofsingle self cooling source. In FIG. 8A, the refractive indices,geometry, and spacing of the LEDs 136, the wavelength conversionelements 133 and 135, and the bonding material 137 will determine thefar field distribution of the source. The far field distribution isdetermined by where the optical rays exit, how much of the optical rays,the direction of the optical rays and the spectrum of optical rays thatexit a particular spatial point on the single self cooling source. FIG.8 illustrates various reflectors, scattering elements, and diffuserswhich modify where, how much, which way and the spectrum of the lightrays emitted from the source. One or more wavelength conversion elementsfor mounting LEDs 136 can be used although two wavelength conversionelements 133 and 135 are depicted. Multiple LEDs 136 can be mounted onone or more surface of the one wavelength conversion element 133. Basedon these parameters, radiation will be emitted from the structure orlight guided within the source. Additionally, edge element 134 may alsomodify the far field distribution out of the device. Edge element 134and bonding materials 137 may be translucent, transparent, opaque,and/or luminescent. Luminescent powders within a transparent matrix foredge element 134 and bonding materials 137 can modify the emissionspectrum as well as the far field intensity distribution.

FIG. 8B depicts a self cooling light source where the entire end of theself cooling light source is substantially covered with a scatteringelement 139 within a matrix 138. Additionally, scattering element 139and matrix 138 may extend to encompass not only edges of the selfcooling light source but also a substantial portions of the othersurfaces of the self cooling light source. In this manner, light emittedfrom all the surface of the self cooling light source can be redirectedto modify the far field intensity distribution. Luminescent materialsfor scattering element 139 are excited by at least a portion of thespectrum emitted by the self cooling light source.

FIG. 8C depicts edge turning element 140 consisting of metal, diffusescatterer, dielectric mirror, and/or translucent material whereby atleast a portion of the light generated within the LED or wavelengthconversion elements are redirected as depicted in ray 141.

FIG. 8D depicts an outer coating 142 which may be translucent, partiallyopaque, polarized, and/or luminescent. The far field intensity,polarization, and wavelength distribution can be modified both in thenear field and far field and spatial information can be imparted ontothe self cooling light source. As an example, a self cooling lightsource with a shape similar to a candle flame may have a spectrallyvariable outer coating 142 such that red wavelengths are emitted morereadily near the tip of the candle flame and blue wavelengths areemitted more readily near the base of the candle flame. In this fashion,the spatially spectral characteristics of a candle flame could be moreclosely matched. Using this technique a wide range of decorative lightsources can be formed without the need for additional optical elements.

In another example, outer coating 142 may consist of a reflectivecoating such as aluminum into which openings are etched or mechanicallyformed. More specifically, sunlight readable indicator lights can beformed using this technique as warning, emergency, or cautionaryindicators. The use of circular polarizers within outer coating 142 canenhance sunlight readability. Alternately, outer coating 142 could bepatterned to depict a pedestrian crossing symbol that could be eitherdirect viewed or viewed through an external optic thereby creating aultra compact warning sign for crosswalks and other traffic relatedapplications. In another example, outer coating 142 may consist ofspectrally selective emissivity coating such that the emissivity of theself cooling light source is enhanced for wavelengths longer than 700nm. By enhancing the infrared and far infrared emissivity of the selfcooling light source more efficient light sources can be realized. Asstated in the previous example of FIG. 3 the radiation coolingrepresents a significant percentage of the cooling in self cooling lightsources. It is preferred that high emissivity coatings be used for outercoating 142 to maximize cooling from the surface of the self coolinglight source. Most preferred is an outer coating 142 with an emissivitygreater than 0.5. Depending on the maximum surface temperature theradiative cooling can represent between 20% and 50% of the heatdissipation of the source.

FIG. 9A depicts the use of die shaping of optical devices within a media143. As an example, LED 145 contains an active region 146 embeddedwithin media 143. Using ray tracing techniques known in the art, thereis an optimum angle 144 to maximize the amount of radiation transferredinto media 143. Typically, semiconductor materials exhibit highrefractive index, which tends to lead to light trapping within the LED145. In FIG. 9A the optimum angle 144 subtends the active region 146 asshown in the figure.

Alternately, FIG. 9B depicts that surfaces 149, 148 and 147 may benon-orthogonal forming a non square or rectangular die. In both thesecases, light trapped within the LED 150 can more efficiently escape thedie. The use of both forms of die shaping together is preferred. The useof non-rectangular shapes for LED 150 embedded within a wavelengthconversion element to enhance extraction efficiency is a preferredembodiment of this invention.

FIG. 10A depicts different mounting methods for LEDs 152 and 154 withinwavelength conversion element 151 and the use of bonding layers 153 and155. Bonding layers 153 and 155 thermally, optically, and mechanicallyattach LEDs 152 and 154 to at least one surface of wavelength conversionelement 151. LED 152 is at least partially embedded within wavelengthconversion element 151 which can allow for both edge and surfacecoupling of radiation emitted by the LED 152 into wavelength conversionelement 151 using bonding layer 153. Alternately, LED 154 issubstantially coupled to the surface of wavelength conversion element151 using bonding layer 155. Bonding layers 55 and 153 may be eliminatedwhere wavelength conversion element 151 is directly bondable to LEDs 154and 152 using wafer boding, fusion bonding, or melt bonding.

FIG. 10B depicts a typical transmission spectrum 157 of wavelengthconversion elements. Blue emission 156 is absorbed by the wavelengthconversion element and then reemitted at longer wavelengths. Redemission 158 is typically not strongly absorbed and therefore behaves asif the wavelength conversion element 151 is simply a waveguide.Virtually any color light source can be realized by properly selectingthe right combination of blue and red LEDs within the wavelengthconversion element 151. While wavelength conversion is a preferredembodiment, FIG. 10B illustrates that self-cooling light sources do notrequire that the wavelength conversion element 151 be luminescent. Inthe case of a red self-cooling light source, wavelength conversionelement 151 may be used to optically distribute and thermally cool theLEDS without wavelength conversion. Alternately, UV responsiveluminescent materials can be used for wavelength conversion element 162with UV LEDs 164 or 165. The transmission spectrum 157 is shifted toshorter wavelength which allows for the formation of self cooling lightsources which exhibit white body colors, as seen in fluorescent lightsources. This wavelength shift however is offset by somewhat reducedefficiency due to larger stokes shift losses.

FIG. 11 depicts a color tunable self-cooling light source containing atleast one wavelength conversion element 162 with an electricalinterconnect 168, at least one blue LED 164, at least one red LED 163,and drive electronics 165, 166, and 167. Electrical interconnect 168 isa thick film printed silver ink. Three separate pins 159, 160, and 161to provide independent control of blue led 164 from red LED 163. Pins159, 160, and 161 can be physically shaped to allow for keying therebyensuring that the self-cooling light source is properly connected toexternal power sources. While pins 159, 160 and 161 are substantiallyshown on the same side of wavelength conversion element 162, the use ofalternate pin configurations are anticipated by the inventors. Ingeneral, external electrical interconnect can be accomplished via pins159, 160, and 161 as shown in FIG. 11 or via alternate interconnectmeans including, but not limited to, flex circuits, rigid elementscontaining electrical traces, coaxial wires, shielded and unshieldedtwisted pairs, and edge type connectors on or connected to wavelengthconversion element 162 are embodiments of this invention. Additionallyfeedthroughs within wavelength conversion element 162 can be formed viamechanical, chemical etching, laser, waterjet, or other subtractivemeans to form external interconnects to any of the previous listedelectrical interconnect elements in any plane of the wavelengthconversion element 162. Drive electronics 165, 166, and 167 may consistof both active and passive elements ranging from resistors, caps, andinductors. In this manner, a variety of external drive inputs can beused to excite the light source. As an example, a current source chipmay be mounted onto the wavelength conversion element 162 and connectedto an external voltage source via pins 159,160, and 161. As known in theart, typical current source chips can also have an external resistor,which sets the current, which flows through the current source chip. Theexternal resistor may be mounted on the wavelength conversion element162 or be external to the source and connected to current source chipvia pins 159, 160, and 161. As the functionality within the light sourceincreases, the number pins may be increased. Integrated circuits can beused for drive electronics 165, 166, and/or 167. Wavelength conversionelement 162 also substantially cools the drive electronics 165, 166, and167 as well as LEDs 164 and 165. Pins 159, 160, and 161 may be used toremove heat from the heat generating elements of the light source.Wavelength conversion element 162 is luminescent and provides foroptical diffusion and cooling of the heat generating elements within theself cooling light source. In this case, additional wavelength emittersmay be added including, but not limited to, UV, violet, cyan, green,yellow, orange, deep red, and infrared

FIG. 12 depicts a self cooling light source with an embedded activedriver 172 capable of driving multiple LEDs 171, all of which aremounted and cooled substantially by wavelength conversion element 169.Input pins 170 may provide power input to active driver 172 but alsoprovide outputs including, but not limited to, light source temperature,ambient temperature, light output levels, motion detection, infraredcommunication links, and dimming controls. As previously disclosed, thetransmission spectrum of the wavelength conversion element 169 allowsfor low absorption of longer wavelengths. An infrared/wireless emitterand receiver can be integrated into embedded active driver 172 so thatthe self cooling light source could also serve as a communication linkfor computers, TVs, wireless devices within a room, building, oroutside. This integration eliminates the need for additional wiring anddevices.

FIG. 13A depicts the use of electrical contacts 174 and 175 asadditional thermal conduction paths for extracting heat 178 out of thewavelength conversion elements 173 and 174 additionally cooling pathsfor LED 177. LED 177 may be direct attach or flip chip and may be alateral, vertical, or edge contact die. As an example, electricalcontact 174 and 175 may consist of 0.3 mm thick Tin plated aluminumplates sandwiched between wavelength conversion elements 173 and 174. Inthis manner both electrical input and additional cooling means forwavelength conversion elements 173 and 174 as well as LED 177 can berealized.

FIG. 13B depicts a rod based light source with LEDs 180 within rodshaped wavelength conversion element 182 wherein heat 181 isadditionally extracted via conduction to contacts 178 and 179.Alternately, hemispherical, pyramidal, and other non-flat shapes andcross-sections maybe used for wavelength conversion element 182 tocreate a desired intensity, polarization, and wavelength distribution.Cross-section and other shapes, such as spheres and pyramids, maximizethe surface area to volume ratio, so that convective and radiativecooling off the surface of the wavelength conversion element 182 ismaximized while using the least amount of material possible. As anexample, contacts 178 and 179 may consist of 2 mm copper heatpipesthermally bonded via a bonding method including but not limited togluing, mechanical, soldering, or brazing means to wavelength conversionelement 182. In this manner additional cooling maybe realized. LEDs 180may be mounted on the surface or inside of wavelength conversion element182. As an example LEDs 180 may be mounted on the flat surface of twohemispherical wavelength conversion elements 182. The two hemisphericalwavelength conversion elements 182 are bonded together to form aspherical self cooling light source with the LEDs 180 embedded withinthe wavelength conversion elements 182. Alternately, the LEDs 180 may bemounted on the spherical surface of the hemispherical wavelengthconversion element 182 such the light generated by LED 180 generally iscoupled into the hemispherical wavelength conversion element 182.Optionally, the flat surface of hemispherical wavelength conversion 182may have additional luminescent coatings such that the light emitted byLEDs 180 is effectively coupled by the hemispherical wavelengthconversion element 182 onto the luminescent bonding layer whichreflects, transmits, converts or otherwise emits both the light emittedby the LEDs 180 and any luminescent elements back out of thehemispherical wavelength conversion element 182. The advantage of thisapproach is that the LEDs 180 are mounted closer to the cooling surfaceof the wavelength conversion element, a high degree of mixing ispossible, and the angular distribution of the source can be controlledby how well the bonding layer is index matched to the wavelengthconversion element 182. Bonding two hemispherical wavelength conversionelements 182 together forms a spherical source with externally mountedLEDs 180.

FIG. 14 depicts a self cooling light source with at least two thermallyand/or optically separated zones. Waveguide 183 containing LEDs 184 isoptically and/or thermally isolated via barrier 185 from waveguide 186and LEDs 187. Dual colored light sources can be formed. Alternately,temperature sensitive LEDs such as AlInGaP can be thermally isolatedfrom more temperature stable InGaN LEDs. Waveguide 183 and 186 may ormay not provide luminescent conversion. LEDs 184 are AlInGaP (red) LEDsmounted to waveguide 183 made out of sapphire. LEDs 187 are InGaN blueLEDs mounted onto waveguide 186, which is single crystal Ce:YAG. Thebarrier 185 is a low thermal conductivity alumina casting material.AlinGaP efficiency drops by 40% for junction temperatures over 60degrees C. while InGaN efficiency will drop only by 10% for a similarjunction temperature. White light sources can be realized by thermallyisolating the AlinGap from the InGaN high overall efficiency. Using thisapproach the two sections operate at different surface temperatures. TheInGaN LED 187 and waveguide 186 operates at a higher surface temperaturewhile the AlInGaP LED 184 and waveguide 183 operates at a lower surfacetemperature.

FIG. 15 depicts Blue LED 189 mounted to wavelength conversion element188 and Red LED 192 with driver 190. Power lines 191, 193, 194, and 195and control line 196 are also shown. Red LED 192 drive level is set viacontrol line 196 by controlling the voltage/current flow available viapower line input 191 and output 195. Typically driver 190 would be aconstant current source or variable resistor controlled via control line196. As stated earlier, blue LED 189 is typically InGaN with more stableregarding temperature, life and drive levels than red LED 192 typicallyAlInGaP. As an example, TPA coated with europium doped strontiumthiogallate singularly or as a multiphase with another gallate, such asEu doped magnesium gallate for wavelength conversion element 188 isexcited by 450 nm LED 189. 615 nm AlinGaP red LED 192 is also mounted onthe wavelength conversion element 188 along with driver 190. Heat isspread out via wavelength conversion element 188 as well as theradiation emitted by blue LED 189 and red LED 192. Control line 196 isused to adjust the color temperature of the source within a range byincreasing the current to red LED 192 relative to the fixed output ofblue LED 189. Additional LEDs and other emission wavelengths can beused.

FIG. 16 depicts a white light spectrum for a typical solid state lightsource. FIG. 16A illustrates high color temperature low CRI spectrum 197typically created by blue LEDS and Ce:YAG phosphors. Additionalphosphors are typically added to add more red content in order to lowerthe color temperature as shown in spectrum 198. This red additionhowever requires that a portion of the blue and in some cases some ofthe green be absorbed which reduces overall efficiency.

FIG. 16B depicts the typical spectrum 199 from a blue LED, Ce:YAGphosphor, and red LED. The red LED spectrum is additive as shown inspectrum 200. In general, both methods of FIG. 16 are used to formself-cooling light source described in this invention.

FIG. 17 depicts a high CRI white light spectrum 201 formed by mixingphosphor and LED spectrums A, B, C, D, and E. Spectral ranges can bemixed, diffused and converted within the wavelength conversion elementsdisclosed in this invention in addition to cooling, mechanicallymounting, environmentally protecting, and electrically interconnectingthe devices needed to generate the spectrums depicted. As an example,spectrum B may be derived from a blue 440 nm emitting LED, a portionwhose output is used to excite a single crystal Ce:YAG luminescentelement as previously disclosed to form spectrum A between 500 nm and600 nm. Spectrum C may consist of a cyan quantum dot which also convertsa portion of output of the blue 440 nm emitting LED into 490 to 500 nmwavelengths. Spectrum D maybe produced by using a wavelength shifter diesuch as Eljen-284 (Eljen Technologies Inc.) to convert a portion ofSpectrum A into wavelengths between 580 nm and 700 nm and Spectrum Emaybe a AlinGap red LED emitting between 600 and 800 nm. Infraredemitters or converters may also be add for communication links,security, and night vision applications.

FIG. 18 depicts various shapes of waveguides and luminescent coatings.FIG. 18A depicts a textured thermally conductive waveguide 203 with aluminescent coating 202. As an example, a micro lens array may be presssintered out of TPA and coated with Ce:YAG via flamespraying. FIG. 18Bdepicts an EFG formed single crystal Ce:YAG rod 204 coated with a highemissivity coating 205 with a refractive index substantially equal tothe geometric mean of Ce:YAG and air and a thickness greater than 300angstroms. In the previous example of FIG. 3 the importance of radiativecooling even at low surface temperatures is disclosed. In this examplethe radiative cooling can represent up to 30% of the total heatdissipated as long as the emissivity of the surface is above 0.8.Emissivity varies from very low (0.01) for polished metals to very high0.98 for carbon black surfaces. The use of high emissivity coatings 205that are also transparent in the visible spectrum are most preferred.These include but not limited to silicates, glasses, organics, nitrides,oxynitrides, and oxides. Even more preferred is high emissivity coating205 that also exhibits a thermal conductivity greater than 1 W/m/K. Thehigh emissivity coating 205 thickness is preferably between 1000angstroms and 5 microns thick. The emissivity coating 205 may also beluminescent.

FIG. 19A depicts a self cooling light source 206 and an optic 207. Optic207 may be reflective, transparent, translucent or opaque. Bothdecorative and directional means may be used as an optic. Parabolic,elliptical, non-imaging and other optical configuration as known in theart may be used as an optic. In particular, the use of prismatic surfaceelements on optic 207 wherein a substantial portion of the light emittedby self cooling light source 206 are redirected in a directionorthogonal to their original direction are embodiments of thisinvention. Optic 207 redirects a portion of the light from light source206 downward. The optic 207 may consist of, but is not limited to,glass, single crystal, polymer or other translucent/transparentmaterials. Colored translucent/transparent materials create a specificdecorative or functional appearance. As an example a light source 206may be embedded into an orange glass glob to form a decorative lamp. Theelimination of the need for a heatsink greatly simplifies the opticaldesign and allows for a wider range of reflectors and optical elements.

Alternately, FIG. 19B depicts an external movable reflector 209 whichslides 210 up and down light source 208. Using this approach thepercentage of downward light can be adjusted relative to the amount ofdiffuse lighting. Again the elimination of heatsinks and the formationof an extended source greatly simplifies the optical design of the lightfixture.

FIG. 20 depicts methods of adjusting the far field distributions ofsingle light sources. In FIG. 20A, the far field distribution bothintensity and wavelength can be adjusted by mounting methods for theLEDs 214 and 216 within or onto wavelength conversion element 211. LED214 depicts an embedded LED 214 in which a pocket or depression isformed in wavelength conversion element 211. This embedded LED changesthe ratio of transmitted rays 212 to waveguided rays 213 relative tosurface mounted LED 216 which has a substantially different ratio oftransmitted rays 217 to waveguided rays 218.

In FIG. 20B an optic 220 extracts light off of more than one surface oflight source 219. In this case, rays 221 are redirected substantiallyorthogonally to the surface the rays were emitted from and mixed withthe rays from other surfaces of light source 219. The optic 220 may be aprism, lens, parabolic, elliptical, asperical, or free formed shape.

FIG. 20C depicts embedded LEDs 225 in embedded occlusions 226 withedge-turning elements 224 which were previously disclosed. Rays 227 and223 can be directed substantially orthogonally out of the wavelengthconversion element 222.

FIG. 21A depicts a LED die 230 bonded into a wavelength conversionelement containing depressions or pockets 228 using a bonding layer 229,a electrical interconnect layer 231 and protective dielectric layer 232.As an example, a 500 microns thick Ce:YAG single crystal wafer is laserdrilled to have a pocket into which lateral LED die 230 is placed andbonded using a polysilazane. The polysilizane is at least partiallycured. The polysilizane is further coated using inkjet printingtechniques to cover all but the metal contact pads of lateral LED die230. Conductive ink is printed via, but not limited to, inkjet,screenprinting, tampo, or lithographic means such that the exposed metalcontact pads of lateral LED die 230 are interconnected electrically viaelectrical interconnect layer 231. Nanosilver, silver paste, and otherhighly reflective printable electrically conductive inks, pastes orcoatings are the preferred conductive ink. A protective dielectric layer232 is applied via, but not limited to, inkjet, spin coating, dipcoating, slot coating, roll coating and evaporative coating means.

FIG. 21B depicts LED 233 mounted to the surface of waveguide 234 most ofthe rays do not couple to the waveguide efficiently. FIG. 21C depictsembedded LED 235 within a pocket in waveguide 236. Optically andthermally there is more coupling into waveguide 236. In addition the useof embedded LED 235 allows for simplified interconnect as depicted inFIG. 21A. Further luminescent insert 237 may be used to convert at leasta portion of the spectrum from LED 233 or 235. In this case lower costmaterials may be used for waveguide 234 and 236 respectively. As anexample, single crystal Ce:YAG inserts 50 microns thick with a Ce dopingconcentration greater than 0.2% with substantially the same area asembedded LED 235 can be inserted into press sintered TPA waveguides. Inthis manner, the amount of luminescent material can be minimized whilestill realizing the benefit of a thermally conductive element including,but not limited to, waveguide, increased thermal cooling surface, andoptical spreading of the light over an area larger than eitherluminescent insert 237 or LED 235. Ceramic, polycrystalline, amorphous,composite and pressed powders of luminescent materials may be used forluminescent insert 237. A waveguide 236 with a thermal conductivitygreater than 1 W/m/K can work with a luminescent insert 237. LED 235consists of one or more of the LED which is an InGaN, AlGaN, and/orAlInGaP based LED in waveguide 236 with a thermal conductivity greaterthan 1 W/m/K with at least one luminescent insert 237.

While the invention has been described in conjunction with specificembodiments and examples, it is evident to those skilled in the art thatmany alternatives, modifications and variations will be evident in lightof the foregoing descriptions. Accordingly, the invention is intended toembrace all such alternatives, modifications and variations that fallwithin the spirit and scope of the appended claims.

What is claimed is:
 1. A lighting system comprising: at least oneoptical element; at least one self cooling solid state light sourcewherein said self cooling light source further comprises: at least onelight emitting diode; at least one thermally conductive translucentelement; and at least one light emitting surface on said thermallyconductive translucent element; and wherein said at least one lightemitting surface of said at least one self cooling solid state lightsource provides a substantial portion of the cooling of said at leastone self cooling solid state light source to the surrounding ambient. 2.The lighting system of claim 1 wherein said at least one self coolingsolid state light source exhibits a substantially white body color. 3.The lighting system of claim 1 wherein said at least one self coolingsolid state light source is positioned such that a portion of the lightemitted by said at least one self cooling solid state light sourceimpinges on said at least one optical element.
 4. The lighting system ofclaim 1 further comprising at least two self cooling solid state lightsources which are positioned such that the light emitted by said lightemitting surfaces of said at least two self cooling solid state lightsources impinges at least partially on each other.
 5. The lightingsystem of claim 1 wherein said at least one optical element is one ofthe following; lens, reflector, diffuser, prism, parabolic, elliptical,aspherical, or free form shape.
 6. The lighting system of claim 1wherein said at least one optical element is comprised of coloredmaterials to form a decorative light source.
 7. A solid state lightingsystem comprising multiple solid state light sources wherein each solidstate light source is comprised of at least one light emitting surfacewherein said at least one light emitting surface provides cooling ofsaid solid state light source and wherein said solid state light sourcesand said at least one light emitting surfaces of said multiple solidstate light sources are arranged to enhance convective heat transfer tothe surrounding ambient.
 8. The solid state lighting system of claim 7wherein a minimum spacing of 2 mm is maintained between said lightemitting and said cooling surfaces of adjacent said multiple solid statelight sources.
 9. The solid state lighting system of claim 7 furthercomprising multiple optical elements which facilitate convective heattransfer to the surrounding ambient from said light emitting and coolingsurfaces of said multiple solid state light sources.
 10. The solid statelighting system of claim 9 wherein said convective heat transfer isinduced convective heat transfer.
 11. The solid state lighting system ofclaim 7 further comprising an external frame wherein said external frameprovides both mechanical support and electrical interconnect to said atleast one solid state light sources.
 12. A self cooling color tunablelight source comprising: at least two LEDs emitting substantiallydifferent emission wavelengths with independent electricalinterconnects; at least one thermally conductive light transmittingelement upon which said LEDs are mounted; wherein said at least onethermally conductive light transmitting element has a light emittingsurface and said at least two different emitting wavelength LEDs areseparately adjusted to modify the spectral emission from said lightemitting surface of said at least one thermally conductive lighttransmitting element, and a substantial amount of the heat generated bysaid at least two LEDs is transferred to the surrounding ambient by saidlight emitting surface.
 13. The self cooling color tunable light sourceof claim 12 wherein said at least two LEDS are at least one of thefollowing; InGaN, GaN, AlGaN, AlInGaP, ZnO, AlN, or diamond based lightemitting diodes.